The present invention refers to an apparatus for determining a colour filter value, which is to be used for a specific original for exposing a gradation change paper.
In the production of black-and-white positive prints from negatives showing excessively strong or insufficient contrasts, which are also referred to as too hard or too soft negatives, photographic papers with different gradations, i.e. so called soft and hard photographic papers, are used for correcting these contrast ranges deviating from the desired contrast ranges. It follows that for compensating an excessively hard negative, a so called soft photographic paper will be used, and vice versa. For some time, so called gradation change papers, which are also referred to as multigrade papers, have been used for adjusting the desired contrast in the case of the positive print, the gradation or contrast property of said gradation change papers depending on the wavelength of the exposure light used. Hence, the gradation of such a gradation change paper can be adjusted freely by using various preceding colour filter combinations upon exposing the positive print. At present, the selection of the colour filter values, which are to be used for correcting the contrast range of an excessively hard or of an insufficiently hard negative upon exposing gradation change papers, is carried out by the operator, who will determine the colour filter value and the density in accordance with his judgement of the contrasts of the negative. Since it is, quite naturally, difficult to determine the gradation change, which will result in the desired positive print, by viewing a negative, the final adjustment of the colour filter combination and of the respective colour filter value, which will be required for the optimum gradation change, can in many cases only be effected after having previously made a test print with a first, still incorrect colour filter value which has roughly been estimated by the operator.
In the field of colour print production on the basis of colour originals, in particular colour negatives, the use of a so called video analyzer for determining the colour filter values by means of which a print is produced from a specific original has been common practice for some time. However, such a video analyzer cannot be used for determining the necessary colour filter value for the production of black-and-white prints with a gradation change paper.